This project will explore relationships between candidate neurotransmitters and the types of sensory fibers entering the spinal cord in a model system, the Atlantic stingray, Dasyatis sabina. The advantages of the stingray are(1) an absence of unmyelinate sensory fibers, (2) a separation of sensory and motor fibers in the spinal nerves, and (3) separation of the projections of the coarse and fine myelinated fibers in the spinal cord. Studies of glutamic acid and substance P will be emphasized. The presence or absence of substance P and somatostatin will first be determined. Release of glutamic acid and of the peptides, if present, from the primary afferent terminals will also be characterized. The receptive field properties and fields of termination in the spinal cord of the large and small myelinated fibers will be elucidated. The effects of agonists and antagonists of excitatory amino acids on transmission at the primary afferent terminals and on iontophoretically administered amino acids will be determined. This system may yield a satisfactory demonstration that glutamic acid acts as a neurotransmitter in the central nervous system. This study will enhance our understanding of the sensory pathways into the spinal cords of vertebrates, including man.